This invention relates to a fluid impulse torque tool used in a screw tightening operation and more particularly it relates to a torque tool wherein an air motor is rotated to cause an oil pressure generator to produce a pulse pressure, which is used to tighten screws.
A torque tool using an oil pressure generator has already been proposed (U.S. Pat. No. 3,116,617). This torque tool is adapted to produce an impulse torque by hydraulic means instead of by conventional mechanical means and is characterized by little noise and vibration, as compared with torque tools using mechanical means for producing impulse torques. This hydraulic torque tool has a relief valve attached to an oil pressure pulse generator and is arranged so that when a predetermined tightening force is attained, the relief valve is actuated to allow the working oil in the oil pressure pulse generator to escape as relief oil, thus preventing generation of a pulse pressure above a fixed value. However, the conventional tool has only the function of preventing generation of a pulse pressure above a fixed value but has no function of automatically stopping the rotation of the air motor. As a result, even after the screw tightening operation has been completed, the air motor continues rotating and the pulse generator continues its pulse generating function. This is utterly useless and uneconomical, detracting from the durability of the air motor and oil pressure pulse generator. Further, with this torque tool, it is impossible to detect the completion of screw tightening, which is inconvenient to actual operation.